Mammalian cells are capable of repairing or inactivating DNA monoadducts of certain bifunctional drugs which are thought to kill cells by the formation of DNA crosslinks. Bifunctional drugs such as cis-Pt complexes, chloroethylnitrosoureas and alkylating agents from DNA crosslinks in a 2\step mechanism, involving a slow conversion of DNA monoadducts to interstrand crosslinks. This project seeks to devise a general method for the direct study of crosslinkable DNA monoadducts. A method based on the alkaline elution assay of interstrand crosslinks was devised. Using the new method, potentially crosslinkable monoadducts were demonstrated in cells treated with cis-Pt. Evidence was obtained for the repair or inactivation of crosslinkable DNA monoadducts in cells. Further work will investigate the role of this inactivation as a determinant of drug sensitivity or drug resistance.